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S3 replica

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This commit is contained in:
Ben Johnson
2021-01-13 10:14:54 -07:00
parent faa5765745
commit 57a02a8628
7 changed files with 940 additions and 28 deletions
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36
cmd/litestream/main.go
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@@ -13,6 +13,7 @@ import (
"time"
"github.com/benbjohnson/litestream"
"github.com/benbjohnson/litestream/s3"
"gopkg.in/yaml.v2"
)
@@ -160,6 +161,11 @@ type ReplicaConfig struct {
Name string `yaml:"name"` // name of replica, optional.
Path string `yaml:"path"`
Retention time.Duration `yaml:"retention"`
// S3 settings
AccessKeyID string `yaml:"access-key-id"`
SecretAccessKey string `yaml:"secret-access-key"`
Bucket string `yaml:"bucket"`
}
func registerConfigFlag(fs *flag.FlagSet, p *string) {
@@ -188,6 +194,8 @@ func newReplicaFromConfig(db *litestream.DB, config *ReplicaConfig) (litestream.
switch config.Type {
case "", "file":
return newFileReplicaFromConfig(db, config)
case "s3":
return newS3ReplicaFromConfig(db, config)
default:
return nil, fmt.Errorf("unknown replica type in config: %q", config.Type)
}
@@ -196,11 +204,37 @@ func newReplicaFromConfig(db *litestream.DB, config *ReplicaConfig) (litestream.
// newFileReplicaFromConfig returns a new instance of FileReplica build from config.
func newFileReplicaFromConfig(db *litestream.DB, config *ReplicaConfig) (*litestream.FileReplica, error) {
if config.Path == "" {
return nil, fmt.Errorf("file replica path require for db %q", db.Path())
return nil, fmt.Errorf("%s: file replica path required", db.Path())
}
r := litestream.NewFileReplica(db, config.Name, config.Path)
if v := config.Retention; v > 0 {
r.RetentionInterval = v
}
return r, nil
}
// newS3ReplicaFromConfig returns a new instance of S3Replica build from config.
func newS3ReplicaFromConfig(db *litestream.DB, config *ReplicaConfig) (*s3.Replica, error) {
if config.AccessKeyID == "" {
return nil, fmt.Errorf("%s: s3 access key id required", db.Path())
} else if config.SecretAccessKey == "" {
return nil, fmt.Errorf("%s: s3 secret access key required", db.Path())
} else if config.Region == "" {
return nil, fmt.Errorf("%s: s3 region required", db.Path())
} else if config.Bucket == "" {
return nil, fmt.Errorf("%s: s3 bucket required", db.Path())
}
r := aws.NewS3Replica(db, config.Name)
r.AccessKeyID = config.AccessKeyID
r.SecretAccessKey = config.SecretAccessKey
r.Region = config.Region
r.Bucket = config.Bucket
r.Path = config.Path
if v := config.Retention; v > 0 {
r.RetentionInterval = v
}
return r, nil
}

13
db.go
View File

@@ -117,6 +117,11 @@ func NewDB(path string) *DB {
return db
}
// SQLDB returns a reference to the underlying sql.DB connection.
func (db *DB) SQLDB() *sql.DB {
return db.db
}
// Path returns the path to the database.
func (db *DB) Path() string {
return db.path
@@ -181,7 +186,7 @@ func (db *DB) CurrentShadowWALIndex(generation string) (index int, size int64, e
if !strings.HasSuffix(fi.Name(), WALExt) {
continue
}
if v, _, _, err := ParseWALPath(fi.Name()); err != nil {
if v, _, _, _, err := ParseWALPath(fi.Name()); err != nil {
continue // invalid wal filename
} else if v > index {
index = v
@@ -478,7 +483,7 @@ func (db *DB) cleanWAL() error {
return err
}
for _, fi := range fis {
if idx, _, _, err := ParseWALPath(fi.Name()); err != nil || idx >= min {
if idx, _, _, _, err := ParseWALPath(fi.Name()); err != nil || idx >= min {
continue
}
if err := os.Remove(filepath.Join(dir, fi.Name())); err != nil {
@@ -858,7 +863,7 @@ func (db *DB) syncWAL(info syncInfo) (newSize int64, err error) {
// Parse index of current shadow WAL file.
dir, base := filepath.Split(info.shadowWALPath)
index, _, _, err := ParseWALPath(base)
index, _, _, _, err := ParseWALPath(base)
if err != nil {
return 0, fmt.Errorf("cannot parse shadow wal filename: %s", base)
}
@@ -1217,7 +1222,7 @@ func (db *DB) checkpointAndInit(info syncInfo, mode string) error {
}
// Parse index of current shadow WAL file.
index, _, _, err := ParseWALPath(info.shadowWALPath)
index, _, _, _, err := ParseWALPath(info.shadowWALPath)
if err != nil {
return fmt.Errorf("cannot parse shadow wal filename: %s", info.shadowWALPath)
}

1
go.mod
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@@ -3,6 +3,7 @@ module github.com/benbjohnson/litestream
go 1.15
require (
github.com/aws/aws-sdk-go v1.27.0
github.com/mattn/go-sqlite3 v1.14.5
github.com/prometheus/client_golang v1.9.0
gopkg.in/yaml.v2 v2.4.0

2
go.sum
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@@ -18,6 +18,7 @@ github.com/armon/go-metrics v0.0.0-20180917152333-f0300d1749da/go.mod h1:Q73ZrmV
github.com/armon/go-radix v0.0.0-20180808171621-7fddfc383310/go.mod h1:ufUuZ+zHj4x4TnLV4JWEpy2hxWSpsRywHrMgIH9cCH8=
github.com/aryann/difflib v0.0.0-20170710044230-e206f873d14a/go.mod h1:DAHtR1m6lCRdSC2Tm3DSWRPvIPr6xNKyeHdqDQSQT+A=
github.com/aws/aws-lambda-go v1.13.3/go.mod h1:4UKl9IzQMoD+QF79YdCuzCwp8VbmG4VAQwij/eHl5CU=
github.com/aws/aws-sdk-go v1.27.0 h1:0xphMHGMLBrPMfxR2AmVjZKcMEESEgWF8Kru94BNByk=
github.com/aws/aws-sdk-go v1.27.0/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
github.com/aws/aws-sdk-go-v2 v0.18.0/go.mod h1:JWVYvqSMppoMJC0x5wdwiImzgXTI9FuZwxzkQq9wy+g=
github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
@@ -124,6 +125,7 @@ github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpO
github.com/hudl/fargo v1.3.0/go.mod h1:y3CKSmjA+wD2gak7sUSXTAoopbhU08POFhmITJgmKTg=
github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
github.com/influxdata/influxdb1-client v0.0.0-20191209144304-8bf82d3c094d/go.mod h1:qj24IKcXYK6Iy9ceXlo3Tc+vtHo9lIhSX5JddghvEPo=
github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af h1:pmfjZENx5imkbgOkpRUYLnmbU7UEFbjtDA2hxJ1ichM=
github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af/go.mod h1:Nht3zPeWKUH0NzdCt2Blrr5ys8VGpn0CEB0cQHVjt7k=
github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
github.com/jpillora/backoff v1.0.0/go.mod h1:J/6gKK9jxlEcS3zixgDgUAsiuZ7yrSoa/FX5e0EB2j4=

24
litestream.go
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@@ -52,8 +52,8 @@ type SnapshotInfo struct {
CreatedAt time.Time
}
// filterSnapshotsAfter returns all snapshots that were created on or after t.
func filterSnapshotsAfter(a []*SnapshotInfo, t time.Time) []*SnapshotInfo {
// FilterSnapshotsAfter returns all snapshots that were created on or after t.
func FilterSnapshotsAfter(a []*SnapshotInfo, t time.Time) []*SnapshotInfo {
other := make([]*SnapshotInfo, 0, len(a))
for _, snapshot := range a {
if !snapshot.CreatedAt.Before(t) {
@@ -63,8 +63,8 @@ func filterSnapshotsAfter(a []*SnapshotInfo, t time.Time) []*SnapshotInfo {
return other
}
// findMinSnapshotByGeneration finds the snapshot with the lowest index in a generation.
func findMinSnapshotByGeneration(a []*SnapshotInfo, generation string) *SnapshotInfo {
// FindMinSnapshotByGeneration finds the snapshot with the lowest index in a generation.
func FindMinSnapshotByGeneration(a []*SnapshotInfo, generation string) *SnapshotInfo {
var min *SnapshotInfo
for _, snapshot := range a {
if snapshot.Generation != generation {
@@ -229,17 +229,18 @@ func IsWALPath(s string) bool {
// ParseWALPath returns the index & offset for the WAL file.
// Returns an error if the path is not a valid snapshot path.
func ParseWALPath(s string) (index int, offset int64, ext string, err error) {
func ParseWALPath(s string) (index int, offset, sz int64, ext string, err error) {
s = filepath.Base(s)
a := walPathRegex.FindStringSubmatch(s)
if a == nil {
return 0, 0, "", fmt.Errorf("invalid wal path: %s", s)
return 0, 0, 0, "", fmt.Errorf("invalid wal path: %s", s)
}
i64, _ := strconv.ParseUint(a[1], 16, 64)
off64, _ := strconv.ParseUint(a[2], 16, 64)
return int(i64), int64(off64), a[3], nil
sz64, _ := strconv.ParseUint(a[3], 16, 64)
return int(i64), int64(off64), int64(sz64), a[4], nil
}
// FormatWALPath formats a WAL filename with a given index.
@@ -248,14 +249,15 @@ func FormatWALPath(index int) string {
return fmt.Sprintf("%016x%s", index, WALExt)
}
// FormatWALPathWithOffset formats a WAL filename with a given index & offset.
func FormatWALPathWithOffset(index int, offset int64) string {
// FormatWALPathWithOffsetSize formats a WAL filename with a given index, offset & size.
func FormatWALPathWithOffsetSize(index int, offset, sz int64) string {
assert(index >= 0, "wal index must be non-negative")
assert(offset >= 0, "wal offset must be non-negative")
return fmt.Sprintf("%016x_%016x%s", index, offset, WALExt)
assert(sz >= 0, "wal size must be non-negative")
return fmt.Sprintf("%016x_%016x_%016x%s", index, offset, sz, WALExt)
}
var walPathRegex = regexp.MustCompile(`^([0-9a-f]{16})(?:_([0-9a-f]{16}))?(.wal(?:.gz)?)$`)
var walPathRegex = regexp.MustCompile(`^([0-9a-f]{16})(?:_([0-9a-f]{16})_([0-9a-f]{16}))?(.wal(?:.gz)?)$`)
// isHexChar returns true if ch is a lowercase hex character.
func isHexChar(ch rune) bool {

18
replica.go
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@@ -333,7 +333,7 @@ func (r *FileReplica) WALs(ctx context.Context) ([]*WALInfo, error) {
// Iterate over each WAL file.
for _, fi := range fis {
index, offset, _, err := ParseWALPath(fi.Name())
index, offset, _, _, err := ParseWALPath(fi.Name())
if err != nil {
continue
}
@@ -446,7 +446,7 @@ func (r *FileReplica) CalcPos(generation string) (pos Pos, err error) {
index := -1
for _, fi := range fis {
if idx, _, _, err := ParseWALPath(fi.Name()); err != nil {
if idx, _, _, _, err := ParseWALPath(fi.Name()); err != nil {
continue // invalid wal filename
} else if index == -1 || idx > index {
index = idx
@@ -679,7 +679,7 @@ func (r *FileReplica) WALIndexAt(ctx context.Context, generation string, maxInde
for _, fi := range fis {
// Read index from snapshot filename.
idx, _, _, err := ParseWALPath(fi.Name())
idx, _, _, _, err := ParseWALPath(fi.Name())
if err != nil {
continue // not a snapshot, skip
} else if !timestamp.IsZero() && fi.ModTime().After(timestamp) {
@@ -783,7 +783,7 @@ func (r *FileReplica) EnforceRetention(ctx context.Context) (err error) {
if err != nil {
return fmt.Errorf("cannot obtain snapshot list: %w", err)
}
snapshots = filterSnapshotsAfter(snapshots, time.Now().Add(-r.RetentionInterval))
snapshots = FilterSnapshotsAfter(snapshots, time.Now().Add(-r.RetentionInterval))
// If no retained snapshots exist, create a new snapshot.
if len(snapshots) == 0 {
@@ -801,7 +801,7 @@ func (r *FileReplica) EnforceRetention(ctx context.Context) (err error) {
}
for _, generation := range generations {
// Find earliest retained snapshot for this generation.
snapshot := findMinSnapshotByGeneration(snapshots, generation)
snapshot := FindMinSnapshotByGeneration(snapshots, generation)
// Delete generations if it has no snapshots being retained.
if snapshot == nil {
@@ -863,7 +863,7 @@ func (r *FileReplica) deleteGenerationWALBefore(ctx context.Context, generation
}
for _, fi := range fis {
idx, _, _, err := ParseWALPath(fi.Name())
idx, _, _, _, err := ParseWALPath(fi.Name())
if err != nil {
continue
} else if idx >= index {
@@ -910,9 +910,3 @@ func compressFile(src, dst string, uid, gid int) error {
// Move compressed file to final location.
return os.Rename(dst+".tmp", dst)
}
// walDirMask is a mask used to group 64K wal files into a directory.
const (
walDirFileN = 0x10000
walDirMask = uint64(0xFFFFFFFFFFFFFFFF ^ (walDirFileN - 1))
)

874
s3/s3.go Normal file
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@@ -0,0 +1,874 @@
package aws
import (
"compress/gzip"
"context"
"fmt"
"io"
"io/ioutil"
"log"
"math"
"os"
"path"
"sync"
"time"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/session"
"github.com/aws/aws-sdk-go/service/s3"
"github.com/aws/aws-sdk-go/service/s3/s3manager"
"github.com/benbjohnson/litestream"
)
const (
DefaultRetentionInterval = 1 * time.Hour
)
var _ litestream.Replica = (*Replica)(nil)
// Replica is a replica that replicates a DB to an S3 bucket.
type Replica struct {
db *litestream.DB // source database
name string // replica name, optional
s3 *s3.S3 // s3 service
uploader *s3manager.Uploader
mu sync.RWMutex
pos litestream.Pos // last position
wg sync.WaitGroup
ctx context.Context
cancel func()
// AWS authentication keys.
AccessKeyID string
SecretAccessKey string
// S3 bucket information
Region string
Bucket string
Path string
// Time to keep snapshots and related WAL files.
// Database is snapshotted after interval and older WAL files are discarded.
RetentionInterval time.Duration
// If true, replica monitors database for changes automatically.
// Set to false if replica is being used synchronously (such as in tests).
MonitorEnabled bool
}
// NewReplica returns a new instance of Replica.
func NewReplica(db *litestream.DB, name string) *Replica {
return &Replica{
db: db,
name: name,
cancel: func() {},
RetentionInterval: DefaultRetentionInterval,
MonitorEnabled: true,
}
}
// Name returns the name of the replica. Returns the type if no name set.
func (r *Replica) Name() string {
if r.name != "" {
return r.name
}
return r.Type()
}
// Type returns the type of replica.
func (r *Replica) Type() string {
return "file"
}
// LastPos returns the last successfully replicated position.
func (r *Replica) LastPos() litestream.Pos {
r.mu.RLock()
defer r.mu.RUnlock()
return r.pos
}
// GenerationDir returns the path to a generation's root directory.
func (r *Replica) GenerationDir(generation string) string {
return path.Join("/", r.Path, "generations", generation)
}
// SnapshotDir returns the path to a generation's snapshot directory.
func (r *Replica) SnapshotDir(generation string) string {
return path.Join("/", r.Path, r.GenerationDir(generation), "snapshots")
}
// SnapshotPath returns the path to a snapshot file.
func (r *Replica) SnapshotPath(generation string, index int) string {
return path.Join(r.SnapshotDir(generation), fmt.Sprintf("%016x.snapshot.gz", index))
}
// MaxSnapshotIndex returns the highest index for the snapshots.
func (r *Replica) MaxSnapshotIndex(generation string) (int, error) {
snapshots, err := r.Snapshots(context.Background())
if err != nil {
return 0, err
}
index := -1
for _, snapshot := range snapshots {
if snapshot.Generation != generation {
continue
} else if index == -1 || snapshot.Index > index {
index = snapshot.Index
}
}
if index == -1 {
return 0, fmt.Errorf("no snapshots found")
}
return index, nil
}
// WALDir returns the path to a generation's WAL directory
func (r *Replica) WALDir(generation string) string {
return path.Join(r.GenerationDir(generation), "wal")
}
// WALPath returns the path to a WAL file.
func (r *Replica) WALPath(generation string, index int) string {
return path.Join(r.WALDir(generation), fmt.Sprintf("%016x.wal", index))
}
// Generations returns a list of available generation names.
func (r *Replica) Generations(ctx context.Context) ([]string, error) {
if err := r.Init(ctx); err != nil {
return nil, err
}
var generations []string
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(path.Join("/", r.Path, "generations")),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
key := path.Base(*obj.Key)
if !litestream.IsGenerationName(key) {
continue
}
generations = append(generations, key)
}
return true
}); err != nil {
return nil, err
}
return generations, nil
}
// GenerationStats returns stats for a generation.
func (r *Replica) GenerationStats(ctx context.Context, generation string) (stats litestream.GenerationStats, err error) {
if err := r.Init(ctx); err != nil {
return stats, err
}
// Determine stats for all snapshots.
n, min, max, err := r.snapshotStats(generation)
if err != nil {
return stats, err
}
stats.SnapshotN = n
stats.CreatedAt, stats.UpdatedAt = min, max
// Update stats if we have WAL files.
n, min, max, err = r.walStats(generation)
if err != nil {
return stats, err
} else if n == 0 {
return stats, nil
}
stats.WALN = n
if stats.CreatedAt.IsZero() || min.Before(stats.CreatedAt) {
stats.CreatedAt = min
}
if stats.UpdatedAt.IsZero() || max.After(stats.UpdatedAt) {
stats.UpdatedAt = max
}
return stats, nil
}
func (r *Replica) snapshotStats(generation string) (n int, min, max time.Time, err error) {
var generations []string
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(r.SnapshotDir(generation)),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
if !litestream.IsSnapshotPath(*obj.Key) {
continue
}
modTime := obj.LastModified.UTC()
n++
if min.IsZero() || modTime.Before(min) {
min = modTime
}
if max.IsZero() || modTime.After(max) {
max = modTime
}
}
return true
}); err != nil {
return n, min, max, err
}
return n, min, max, nil
}
func (r *Replica) walStats(generation string) (n int, min, max time.Time, err error) {
var generations []string
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(r.WALDir(generation)),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
if !litestream.IsWALPath(*obj.Key) {
continue
}
modTime := obj.LastModified.UTC()
n++
if min.IsZero() || modTime.Before(min) {
min = modTime
}
if max.IsZero() || modTime.After(max) {
max = modTime
}
}
return true
}); err != nil {
return n, min, max, err
}
return n, min, max, nil
}
// Snapshots returns a list of available snapshots in the replica.
func (r *Replica) Snapshots(ctx context.Context) ([]*litestream.SnapshotInfo, error) {
if err := r.Init(ctx); err != nil {
return nil, err
}
generations, err := r.Generations(ctx)
if err != nil {
return nil, err
}
var infos []*litestream.SnapshotInfo
for _, generation := range generations {
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(r.SnapshotDir(generation)),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
key := path.Base(*obj.Key)
index, _, err := litestream.ParseSnapshotPath(key)
if err != nil {
continue
}
infos = append(infos, &litestream.SnapshotInfo{
Name: key,
Replica: r.Name(),
Generation: generation,
Index: index,
Size: *obj.Size,
CreatedAt: obj.LastModified.UTC(),
})
}
return true
}); err != nil {
return nil, err
}
}
return infos, nil
}
// WALs returns a list of available WAL files in the replica.
func (r *Replica) WALs(ctx context.Context) ([]*litestream.WALInfo, error) {
if err := r.Init(ctx); err != nil {
return nil, err
}
generations, err := r.Generations(ctx)
if err != nil {
return nil, err
}
var infos []*litestream.WALInfo
for _, generation := range generations {
var prev *litestream.WALInfo
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(r.WALDir(generation)),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
key := path.Base(*obj.Key)
index, offset, _, _, err := litestream.ParseWALPath(key)
if err != nil {
continue
}
// Update previous record if generation & index match.
if prev != nil && prev.Index == index {
prev.Size += *obj.Size
prev.CreatedAt = obj.LastModified.UTC()
continue
}
// Append new WAL record and keep reference to append additional
// size for segmented WAL files.
prev = &litestream.WALInfo{
Name: key,
Replica: r.Name(),
Generation: generation,
Index: index,
Offset: offset,
Size: *obj.Size,
CreatedAt: obj.LastModified.UTC(),
}
infos = append(infos, prev)
}
return true
}); err != nil {
return nil, err
}
}
return infos, nil
}
// Start starts replication for a given generation.
func (r *Replica) Start(ctx context.Context) {
// Ignore if replica is being used sychronously.
if !r.MonitorEnabled {
return
}
// Stop previous replication.
r.Stop()
// Wrap context with cancelation.
ctx, r.cancel = context.WithCancel(ctx)
// Start goroutines to manage replica data.
r.wg.Add(2)
go func() { defer r.wg.Done(); r.monitor(ctx) }()
go func() { defer r.wg.Done(); r.retainer(ctx) }()
}
// Stop cancels any outstanding replication and blocks until finished.
func (r *Replica) Stop() {
r.cancel()
r.wg.Wait()
}
// monitor runs in a separate goroutine and continuously replicates the DB.
func (r *Replica) monitor(ctx context.Context) {
// Continuously check for new data to replicate.
ch := make(chan struct{})
close(ch)
var notify <-chan struct{} = ch
for {
select {
case <-ctx.Done():
return
case <-notify:
}
// Fetch new notify channel before replicating data.
notify = r.db.Notify()
// Synchronize the shadow wal into the replication directory.
if err := r.Sync(ctx); err != nil {
log.Printf("%s(%s): sync error: %s", r.db.Path(), r.Name(), err)
continue
}
}
}
// retainer runs in a separate goroutine and handles retention.
func (r *Replica) retainer(ctx context.Context) {
ticker := time.NewTicker(1 * time.Minute)
defer ticker.Stop()
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
if err := r.EnforceRetention(ctx); err != nil {
log.Printf("%s(%s): retain error: %s", r.db.Path(), r.Name(), err)
continue
}
}
}
}
// CalcPos returns the position for the replica for the current generation.
// Returns a zero value if there is no active generation.
func (r *Replica) CalcPos(generation string) (pos litestream.Pos, err error) {
if err := r.Init(context.Background()); err != nil {
return pos, err
}
pos.Generation = generation
// Find maximum snapshot index.
if pos.Index, err = r.MaxSnapshotIndex(generation); err != nil {
return litestream.Pos{}, err
}
index := -1
var offset int64
if err := r.s3.ListObjectsPages(&s3.ListObjectsInput{
Bucket: aws.String(r.Bucket),
Prefix: aws.String(r.WALDir(generation)),
Delimiter: aws.String("/"),
}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
for _, obj := range page.Contents {
key := path.Base(*obj.Key)
idx, offset, sz, _, err := litestream.ParseWALPath(key)
if err != nil {
continue // invalid wal filename
}
if index == -1 || idx > index {
index, offset = idx, 0 // start tracking new wal
} else if idx == index {
offset += sz // append additional size to wal
}
}
return true
}); err != nil {
return litestream.Pos{}, err
}
if index == -1 {
return pos, nil // no wal files
}
pos.Index = index
pos.Offset = offset
return pos, nil
}
// snapshot copies the entire database to the replica path.
func (r *Replica) snapshot(ctx context.Context, generation string, index int) error {
// Acquire a read lock on the database during snapshot to prevent checkpoints.
tx, err := r.db.SQLDB().Begin()
if err != nil {
return err
} else if _, err := tx.ExecContext(ctx, `SELECT COUNT(1) FROM _litestream_seq;`); err != nil {
tx.Rollback()
return err
}
defer tx.Rollback()
// Open database file handle.
f, err := os.Open(r.db.Path())
if err != nil {
return err
}
defer f.Close()
pr, pw := io.Pipe()
gw := gzip.NewWriter(pw)
go func() { io.Copy(gw, f) }()
snapshotPath := r.SnapshotPath(generation, index)
if _, err := r.uploader.Upload(&s3manager.UploadInput{
Bucket: aws.String(r.Bucket),
Key: aws.String(snapshotPath),
Body: pr,
}); err != nil {
return err
}
return nil
}
// snapshotN returns the number of snapshots for a generation.
func (r *Replica) snapshotN(generation string) (int, error) {
snapshots, err := r.Snapshots(context.Background())
if err != nil {
return 0, err
}
var n int
for _, snapshot := range snapshots {
if snapshot.Generation == generation {
n++
}
}
return n, nil
}
// Init initializes the connection to S3. No-op if already initialized.
func (r *Replica) Init(ctx context.Context) (err error) {
r.mu.Lock()
defer r.mu.Unlock()
if r.s3 != nil {
return nil
}
sess, err := session.NewSession(&aws.Config{Region: aws.String(r.Region)})
if err != nil {
return fmt.Errorf("cannot create aws session: %w", err)
}
r.s3 = s3.New(sess)
r.uploader = s3manager.NewUploader(sess)
return nil
}
func (r *Replica) Sync(ctx context.Context) (err error) {
if err := r.Init(ctx); err != nil {
return err
}
// Find current position of database.
dpos, err := r.db.Pos()
if err != nil {
return fmt.Errorf("cannot determine current generation: %w", err)
} else if dpos.IsZero() {
return fmt.Errorf("no generation, waiting for data")
}
generation := dpos.Generation
// Create snapshot if no snapshots exist for generation.
if n, err := r.snapshotN(generation); err != nil {
return err
} else if n == 0 {
if err := r.snapshot(ctx, generation, dpos.Index); err != nil {
return err
}
}
// Determine position, if necessary.
if r.LastPos().IsZero() {
pos, err := r.CalcPos(generation)
if err != nil {
return fmt.Errorf("cannot determine replica position: %s", err)
}
r.mu.Lock()
r.pos = pos
r.mu.Unlock()
}
// Read all WAL files since the last position.
for {
if err = r.syncWAL(ctx); err == io.EOF {
break
} else if err != nil {
return err
}
}
return nil
}
func (r *Replica) syncWAL(ctx context.Context) (err error) {
rd, err := r.db.ShadowWALReader(r.LastPos())
if err == io.EOF {
return err
} else if err != nil {
return fmt.Errorf("wal reader: %w", err)
}
defer rd.Close()
// Ensure parent directory exists for WAL file.
filename := r.WALPath(rd.Pos().Generation, rd.Pos().Index)
if err := os.MkdirAll(path.Dir(filename), 0700); err != nil {
return err
}
// Create a temporary file to write into so we don't have partial writes.
w, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0600)
if err != nil {
return err
}
defer w.Close()
// Seek, copy & sync WAL contents.
if _, err := w.Seek(rd.Pos().Offset, io.SeekStart); err != nil {
return err
} else if _, err := io.Copy(w, rd); err != nil {
return err
} else if err := w.Sync(); err != nil {
return err
} else if err := w.Close(); err != nil {
return err
}
// Save last replicated position.
r.mu.Lock()
r.pos = rd.Pos()
r.mu.Unlock()
return nil
}
// SnapsotIndexAt returns the highest index for a snapshot within a generation
// that occurs before timestamp. If timestamp is zero, returns the latest snapshot.
func (r *Replica) SnapshotIndexAt(ctx context.Context, generation string, timestamp time.Time) (int, error) {
fis, err := ioutil.ReadDir(r.SnapshotDir(generation))
if os.IsNotExist(err) {
return 0, litestream.ErrNoSnapshots
} else if err != nil {
return 0, err
}
index := -1
var max time.Time
for _, fi := range fis {
// Read index from snapshot filename.
idx, _, err := litestream.ParseSnapshotPath(fi.Name())
if err != nil {
continue // not a snapshot, skip
} else if !timestamp.IsZero() && fi.ModTime().After(timestamp) {
continue // after timestamp, skip
}
// Use snapshot if it newer.
if max.IsZero() || fi.ModTime().After(max) {
index, max = idx, fi.ModTime()
}
}
if index == -1 {
return 0, litestream.ErrNoSnapshots
}
return index, nil
}
// Returns the highest index for a WAL file that occurs before maxIndex & timestamp.
// If timestamp is zero, returns the highest WAL index.
func (r *Replica) WALIndexAt(ctx context.Context, generation string, maxIndex int, timestamp time.Time) (int, error) {
var index int
fis, err := ioutil.ReadDir(r.WALDir(generation))
if os.IsNotExist(err) {
return 0, nil
} else if err != nil {
return 0, err
}
for _, fi := range fis {
// Read index from snapshot filename.
idx, _, _, _, err := litestream.ParseWALPath(fi.Name())
if err != nil {
continue // not a snapshot, skip
} else if !timestamp.IsZero() && fi.ModTime().After(timestamp) {
continue // after timestamp, skip
} else if idx > maxIndex {
continue // after timestamp, skip
} else if idx < index {
continue // earlier index, skip
}
index = idx
}
// If max index is specified but not found, return an error.
if maxIndex != math.MaxInt64 && index != maxIndex {
return index, fmt.Errorf("unable to locate index %d in generation %q, highest index was %d", maxIndex, generation, index)
}
return index, nil
}
// SnapshotReader returns a reader for snapshot data at the given generation/index.
// Returns os.ErrNotExist if no matching index is found.
func (r *Replica) SnapshotReader(ctx context.Context, generation string, index int) (io.ReadCloser, error) {
dir := r.SnapshotDir(generation)
fis, err := ioutil.ReadDir(dir)
if err != nil {
return nil, err
}
for _, fi := range fis {
// Parse index from snapshot filename. Skip if no match.
idx, ext, err := litestream.ParseSnapshotPath(fi.Name())
if err != nil || index != idx {
continue
}
// Open & return the file handle if uncompressed.
f, err := os.Open(path.Join(dir, fi.Name()))
if err != nil {
return nil, err
} else if ext == ".snapshot" {
return f, nil // not compressed, return as-is.
}
// assert(ext == ".snapshot.gz", "invalid snapshot extension")
// If compressed, wrap in a gzip reader and return with wrapper to
// ensure that the underlying file is closed.
r, err := gzip.NewReader(f)
if err != nil {
f.Close()
return nil, err
}
return &gzipReadCloser{r: r, closer: f}, nil
}
return nil, os.ErrNotExist
}
// WALReader returns a reader for WAL data at the given index.
// Returns os.ErrNotExist if no matching index is found.
func (r *Replica) WALReader(ctx context.Context, generation string, index int) (io.ReadCloser, error) {
filename := r.WALPath(generation, index)
// Attempt to read uncompressed file first.
f, err := os.Open(filename)
if err == nil {
return f, nil // file exist, return
} else if err != nil && !os.IsNotExist(err) {
return nil, err
}
// Otherwise read the compressed file. Return error if file doesn't exist.
f, err = os.Open(filename + ".gz")
if err != nil {
return nil, err
}
// If compressed, wrap in a gzip reader and return with wrapper to
// ensure that the underlying file is closed.
rd, err := gzip.NewReader(f)
if err != nil {
f.Close()
return nil, err
}
return &gzipReadCloser{r: rd, closer: f}, nil
}
// EnforceRetention forces a new snapshot once the retention interval has passed.
// Older snapshots and WAL files are then removed.
func (r *Replica) EnforceRetention(ctx context.Context) (err error) {
if err := r.Init(ctx); err != nil {
return err
}
// Find current position of database.
pos, err := r.db.Pos()
if err != nil {
return fmt.Errorf("cannot determine current generation: %w", err)
} else if pos.IsZero() {
return fmt.Errorf("no generation, waiting for data")
}
// Obtain list of snapshots that are within the retention period.
snapshots, err := r.Snapshots(ctx)
if err != nil {
return fmt.Errorf("cannot obtain snapshot list: %w", err)
}
snapshots = litestream.FilterSnapshotsAfter(snapshots, time.Now().Add(-r.RetentionInterval))
// If no retained snapshots exist, create a new snapshot.
if len(snapshots) == 0 {
log.Printf("%s(%s): snapshots exceeds retention, creating new snapshot", r.db.Path(), r.Name())
if err := r.snapshot(ctx, pos.Generation, pos.Index); err != nil {
return fmt.Errorf("cannot snapshot: %w", err)
}
snapshots = append(snapshots, &litestream.SnapshotInfo{Generation: pos.Generation, Index: pos.Index})
}
// Loop over generations and delete unretained snapshots & WAL files.
generations, err := r.Generations(ctx)
if err != nil {
return fmt.Errorf("cannot obtain generations: %w", err)
}
for _, generation := range generations {
// Find earliest retained snapshot for this generation.
snapshot := litestream.FindMinSnapshotByGeneration(snapshots, generation)
// Delete generations if it has no snapshots being retained.
if snapshot == nil {
log.Printf("%s(%s): generation %q has no retained snapshots, deleting", r.db.Path(), r.Name(), generation)
if err := os.RemoveAll(r.GenerationDir(generation)); err != nil {
return fmt.Errorf("cannot delete generation %q dir: %w", generation, err)
}
continue
}
// Otherwise delete all snapshots & WAL files before a lowest retained index.
if err := r.deleteGenerationSnapshotsBefore(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("cannot delete generation %q snapshots before index %d: %w", generation, snapshot.Index, err)
} else if err := r.deleteGenerationWALBefore(ctx, generation, snapshot.Index); err != nil {
return fmt.Errorf("cannot delete generation %q wal before index %d: %w", generation, snapshot.Index, err)
}
}
return nil
}
// deleteGenerationSnapshotsBefore deletes snapshot before a given index.
func (r *Replica) deleteGenerationSnapshotsBefore(ctx context.Context, generation string, index int) (err error) {
dir := r.SnapshotDir(generation)
fis, err := ioutil.ReadDir(dir)
if os.IsNotExist(err) {
return nil
} else if err != nil {
return err
}
for _, fi := range fis {
idx, _, err := litestream.ParseSnapshotPath(fi.Name())
if err != nil {
continue
} else if idx >= index {
continue
}
log.Printf("%s(%s): generation %q snapshot no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
if err := os.Remove(path.Join(dir, fi.Name())); err != nil {
return err
}
}
return nil
}
// deleteGenerationWALBefore deletes WAL files before a given index.
func (r *Replica) deleteGenerationWALBefore(ctx context.Context, generation string, index int) (err error) {
dir := r.WALDir(generation)
fis, err := ioutil.ReadDir(dir)
if os.IsNotExist(err) {
return nil
} else if err != nil {
return err
}
for _, fi := range fis {
idx, _, _, _, err := litestream.ParseWALPath(fi.Name())
if err != nil {
continue
} else if idx >= index {
continue
}
log.Printf("%s(%s): generation %q wal no longer retained, deleting %s", r.db.Path(), r.Name(), generation, fi.Name())
if err := os.Remove(path.Join(dir, fi.Name())); err != nil {
return err
}
}
return nil
}